1. Field of the Invention
The present invention pertains to a process for the separation of a halocarbon and hydrogen fluoride from a mixture of the halocarbon and hydrogen fluoride. More particularly, the invention relates to the separation of azeotropic mixtures of halocarbons and hydrogen fluoride.
2. Description of the Prior Art
It is well known in the art to react hydrogen fluoride with various compounds in order to produce fluorinated halocarbons or fluorocarbons. Such materials are useful as solvents, refrigerants, blowing agents and aerosol propellants, among other uses. Hydrofluorocarbons (HFC's) are a preferred class of halocarbons because they are considered to be much more environmentally advantageous than halocarbons such as hydrochlorofluorocarbons (HCFC's) or chlorofluorocarbons (CFC's) for the reason that they are essentially non-ozone depleting, non-flammable, and non-toxic as compared to chlorine-containing chlorocarbons. In the production of fluorocarbons and HFC's, a typical product stream contains unreacted hydrogen fluoride, other starting reagents, and by-products as well as the desired product. Various conventional separation techniques, for example, distillation and scrubbing, may be used to separate certain by-products and starting materials from a product stream; however, particular difficulty can be experienced in removing halocarbons, including hydrofluorocarbons from hydrogen fluoride. This is especially true for those HFC's having boiling points close to that of HF. In a typical method of preparing hydrofluorocarbons, precursor reagents are fluorinated with hydrogen fluoride. It would be desirable to produce substantially pure hydrofluorocarbons; however, this has proved to be difficult since many hydrofluorocarbons, especially hydrofluorocarbons having three or move carbon atoms, and hydrogen fluoride form azeotropic mixtures which are substantially inseparable by distillation.
The prior art has suggested various methods of separating azeotropic mixtures of hydrofluorocarbons. In this regard, European patent application bearing Publication No. EP 0 472 391 suggests separating HFC-134a from a mixture containing HFC-134a and chlorine-containing HCFC's using an extraction agent such as trichloroethylene or perchloroethylene. European patent application bearing Publication No. EP 0 467 531 teaches a method of separating HFC-134a from a mixture of HFC-134a and HF by passing the mixture through a distillation column to form a residue of pure HFC-134a and then collecting the residue. European patent application bearing Publication No. EP 0 583 551 uses HF to extract a relatively small amount of HF from an HFC-134a/HF azeotrope. HFC-134a is a two carbon fluorocarbon. U.S. Pat. No. 5,211,817 attempts a separation of fluorocarbons from azeotropic mixtures containing HF by column distillation and withdrawing a vapor sidestream followed by introducing the sidestream into a rectifying column equipped with a condenser and operated at a high reflux ratio. Sulfuric acid has been used heretofore to separate a gaseous mixture of HF from a chlorine-containing chlorofluorocarbon, namely FC-22, as described in U.S. Pat. No. 3,873,629. And U.S. Pat. No. 3,947,558 discloses the recovery of HF from C.sub.1 -C.sub.3 halocarbons using a monoglycol. The methods of separation described in the aforementioned publications provide less than satisfactory solutions to the problem.
According to the preferred form of the present invention, there is provided a method for separating a hydrofluorocarbon and hydrogen fluoride from a mixture of the hydrofluorocarbon and hydrogen fluoride by using either water alone or a water/HF mixture as an extracting agent. Although water/HF azeotropic compositions are well known, their use as an extracting agent for the separation of HF from halocarbons such as those which contain three or more carbon atoms is not known. In addition, the use of water as an HF extracting agent for halocarbon is not known.